1. Field of the Invention
The present invention relates to an image forming apparatus operable with a plurality of interconnected on-line sorters each having a plurality of bins, and a control device therefor.
2. Discussion of the Background
Today, a sorter is extensively used with an image forming apparatus, e.g., a stencil printer or an electrophotographic copier, printer or facsimile apparatus. Papers sequentially coming out of the image forming apparatus and each carrying an image thereon are automatically distributed, or sorted, to a plurality of bins arranged in the sorter. This kind of sorter is generally referred to as an on-line sorter. The on-line sorter usually has about twenty bins. A plurality of sorters may be interconnected in an on-line configuration in order to replenish the shortage in the number of bins. Japanese Patent Laid-Open Publication No. 60-248566, for example, discloses in FIG. 3 thereof a stencil printer operable with such on-line sorters. The stencil printer has sorters serially connected to the paper outlet thereof. Each sorter has a bin unit implemented as a stack of bins and movable up and down.
However, the conventional printer with sorters has the following problems to be solved. Assume that the number of printings derived from a single document is small enough to be accommodated in one sorter. Then, all the printings are distributed to the first sorter with the result that the second sorter and successive sorters simply remain idle. Hence, only the first sorter is used every time the printer is operated. Regarding easy take-out of printings, when two on-line sorters are connected to the printer, the first sorter is, of course, inferior to the second sorter. In addition, when all the desired prints are received in the first sorter, it is more difficult to take out the printings from the lower bins than to take them out from the upper bins since the housing of the second sorter gets in the way. While the take-out of printings from the bins of the first sorter will be facilitated if the distance between the first and second sorters is increased, the distance between the sorters should be as short as possible in order to save space.
Another problem with the conventional stencil printer with on-line sorters is that since a printing coming out of the printer carries an excessive amount of ink which is still wet, it smears another printing or is smeared by another printing when distributed to a bin. Specifically, when a printing from the printer is driven out to a tray or a bin over a printing existing there, wet ink on the underlying printing deposits on the underside or rear of the overlying printing and smears it. Further, the overlying printing is moved deeper into the tray or the bin while rubbing the underlying printing with the leading edge thereof. As a result, the rear, particularly leading edge portion, of the overlying printing is noticeably smeared by the underlying printing.
Increasing the interval between the printing and the delivery to a bin as far as possibleis an effective measure against the smears on the rear and leading edges of printings. In this respect, the scond sorter and successive sorters are more desirable than the first sorter since the former has a longer transport distance to the printer than the latter. The longer transport distance translates into a longer transporting time and, therefore, allows the ink to dry. However, it has been customary to automatically distribute printings to the first sorter and then distribute, only when the first sorter becomes full, the other printings to the second sorter and successive sorters.
It follows that when one of the second and successive sorters in used piror to the first sorter, both the easy take-out of printings and the protection of printings from smears of the kind described are achievable. However, this kind of approach brings about another problem that the total printing time increases for the following reasons. First, the bin unit of each sorter usually reaches a home position when it is lowered. A printing operation begins when the bin unit is held in such a home position. As for the first sorter, it should only sequentially raise the bin unit thereof in synchronism with the consecutive printings from the printer. However, when printings should be distributed to the second sorter first, it is necessary to elevate the bin unit of the first conveying unit mounted on the bottom of the bin unit for operation. Second, since the transport distance to the second sorter is longer than the distance to the first sorter, a longer period of time is necessary for a printing to be received in the bin of the second sorter than in the bin of the first sorter.
Another conventional stencil printer operable with sorters has a group mode in addition to a sort mode. In the sort mode, printings derived from a plurality of pages of documents are distributed to each bin in order of page. In the group mode, printings derived from a single document are distributed to bins while being divided into groups each having a desired number of printings. Generally, the group mode is practicable with a minimum number of bins, e.g., twenty bins or less. Hence, while the first sorter is used, the second sorter is not used at all. Moreover, even after printings have been fully sorted by the first sorter, the printer cannot perform the next printing operation unless all the printings are taken out from the bins of the first sorter. This is undesirable in respect of time saving, particularly when urgent printings are desired.
The printer disclosed in, for example, previously mentioned Laid-Open Publication, FIG. 3, has only one non-sort tray. Assume that a number of printings should be produced in a non-sort mode, but the number exceeds the maximum number of printings which can be stacked on the non-sort tray. Then, the operator must take out printings several times in stacks each corresponding to the capacity of the non-sort tray while a printing operation is under way. This is not only troublesome but also forces the operator to stand by the printer until the printing operation ends.